- Direct exchange between every cell and the environment is not possible in all animals
- special structures for exchange & transport needed
- Respiratory systems:
- Circulatory systems:
- Internal transport and gas exchange functionally related
Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. Within the gill filaments, capillary blood flows in the opposite direction to the water
Trachea are a series of tubes that open to the air and connect internally to the circulatory system
Elastic sacs with branching passages into which air is drawn, so that oxygen can pass into the blood and carbon dioxide be removed